t - the object to write to the output message. The type of this object must
have previously been passed to the canWrite method of this
interface, which must have returned true.

type - the (potentially generic) type of object to write. This type must have
previously been passed to the canWrite method of this interface,
which must have returned true. Can be null if not specified.

contentType - the content type to use when writing. May be null to
indicate that the default content type of the converter must be used. If not
null, this media type must have previously been passed to the
canWrite method of this interface, which must have returned
true.